1. Field of the Invention
The invention relates to sludge collectors and, more particularly, relates to sludge collectors which are disposed in holding tanks containing sludge and which employ vertically adjustable weirs to control the flow rate of sludge into the collectors.
2. Discussion of the Related Art
Sludge collectors maybe used in, e.g., municipal waste treatment facilities, citrus and other food preparation facilities, and crude oil treatment facilities to remove floating materials from water or other liquids.
Sludge collectors may also be used in conjunction with spray painting facilities. In such facilities, objects ranging in size from a few square inches to one hundred square feet or more are spray painted in so-called "water wash paint booths" in which a water curtain is established behind the object being painted to remove paint particles from the air being pulled through the water curtain as it is exhausted. The wash water is typically drained into a holding tank where the particles of paint entrained by the water float to the surface where they may form a sludge film or curtain. These paint particles must be removed, particularly if the water from the tank is to be recirculated and reused in the paint booths, since the sludge could otherwise clog the booth recirculating pumps or other water handling components of the booths.
Sludge collectors used in the painting industry or other industries should be located and sized so as to promptly remove the floating materials, along with only as much surface water as is required to flow the materials into the collector. Prompt removal of sludge from the tank is essential to prevent the sludge from becoming saturated and sinking to the bottom of the tank, thus rendering removal more difficult. To oversize a collector is inefficient in terms of equipment, size, cost, as well as operating and maintenance expenses, and generally requires that equipment used in further in-line processing be larger and more expensive than necessary. Thus, attempts have been made to size sludge collectors and the discharge capacities of the pumps removing the sludge from the collectors according to the inflow required to draw floating materials into the collectors. However, pump discharge capacities may vary continuously during use because of, e.g., higher or lower percentages of sludge in the water in the collector. Water levels in the tank may also vary, thus altering the flow rate of sludge into the collector. Thus, the flow rate of the sludge into the collector must be altered to prevent flooding or emptying of the collector upon changes in inflow or outflow rates.
One device which may be used to control the flow rate of sludge into a collector is an adjustable weir positioned at the inlet of a sludge collection box. One such weir is disclosed in U.S. Pat. No. 4,867,872, which issued to Russell et al. on Sep. 19, 1989. The weir disclosed by Russell et al. is part of a weir box or collection box which is slidably mounted on vertical guides and connected to a pneumatic cylinder which can be actuated to raise and lower the weir box in an attempt to vary the depth of the sludge stream flowing into the box. The pneumatic cylinder is actuated, based upon the sensed difference in height between the top of the weir box and the level of water in the tank, in an effort to maintain a constant flow of water into the box.
The mechanism disclosed by Russell et al. exhibits several drawbacks and disadvantages. First, it is relatively complex and expensive to install and to operate because it requires relatively sophisticated sensing and actuating devices. Second, and perhaps more importantly, control of the actuator for the weir is based only upon the sensed sludge level in the tank without taking into account variations in sludge inflow or outflow rates to or from the box caused by variations in pump throughput or the inherent and often accumulative control tolerances of both the level sensor and the weir actuator. A further limitation of the mechanism disclosed by Russell et al. is that manual adjustment of a setscrew is required to even theoretically match the inflow rate to the outflow rate. These problems are further compounded by the fact that the weir box has a tendency to rise when the water level in the box is low and to sink when the water level in the box is high because the box is attached to a pneumatic cylinder the air in which is compressible. These tendencies run directly contrary to the control operations required to adjust inflow to outflows. Thus, depending upon the actual variations of inflow and outflow rates, altering the level of the weir often over-compensates or under-compensates for these variations, leading to an undesirable hunting effect which inevitably degrades the efficiency of the collector.